Lattice site and photoluminescence of erbium implanted in α–Al₂O₃

Single-crystal sapphire (α–Al₂O₃) was implanted at room temperature with 200 keV erbium ions to a fluence of 8 × 10₁₃ cm_–2. Ion channeling using 1.6 MeV He⁺ shows that the crystal suffers little damage for this low dose implant. Angular scans through axial and planar directions in the crystal indicate that 70% of the Er atoms reside on displaced octahedral sites in the α–Al₂O₃ lattice. As pure Al₂O₃ has a high density of free octahedral sites, this explains why high concentrations of Er can be dissolved in this material. Smaller fractions of Er are found on tetrahedral (20%) and random (10%) sites. The samples exhibit strongly peaked photoluminescence spectra around 1.5 μm, due to intra-4f transitions in Er³⁺, indicating the existence of well-defined sites for the luminescing Er³⁺ ions. It is concluded that the octahedral site is the dominating optically active site in the lattice.